The present invention relates generally to clock signal distribution and, more particularly, to a technique for distributing common phase clock signals.
In most present day computer systems, a common clock is used by many different circuits so as to insure synchronous operation among the different circuits. However, when these different circuits are located at different distances away from a common clock source, the clock signals received at the different circuits are typically out of phase with one another. Thus, there has been much interest in finding ways to effectively distribute a clock signal from a common clock source to different circuits within a computer system such that the clock signals received at each circuit are in phase with one another.
The present method for distributing a clock signal from a common clock source to different circuits within a computer system involves the use of H-tree structures, which limit the total number of branches due to a halving of the line characteristic impedance at each branch step. Also, tapped transmission lines and H-tree structures have a limited number of branches or tap points due to the need to keep all branches impedance matched. For example, working back from a load to a source, three branches requires 23 or an 8-fold reduction in line impedance at the driver location. This limits the size of the network. Further, at the lower end of the speed scale, multi-tapped transmission lines suffer from an uncertainty in pulse speed caused by large loading capacitances of connected devices (i.e., causing delays from point to point).
In view of the foregoing, it would be desirable to provide a technique for distributing a clock signal from a common clock source to different circuits within a computer system which overcomes the above-described inadequacies and shortcomings. More particularly, it would be desirable to provide a technique for distributing common phase clock signals to different circuits within a computer system in an efficient and cost effective manner.
According to the present invention, a technique for distributing common phase clock signals is provided. In one embodiment, the technique is realized by providing a forward traveling wave signal and a reverse traveling wave signal on a transmission line, wherein the forward traveling wave signal and the reverse traveling wave signal each have a common frequency and a constant relative phase. The forward traveling wave signal and the reverse traveling wave signal are each tapped off the transmission line at a plurality of different locations along the transmission line. The forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations are then combined so as to form a corresponding plurality of clock signals each having the common frequency and a common phase. The forward traveling wave signal and the reverse traveling wave signal are periodic signals.
In accordance with other aspects of the present invention, the forward traveling wave signal and the reverse traveling wave signal are beneficially provided on the transmission line by applying the forward traveling wave signal to the transmission line, and then reflecting the applied forward traveling wave signal so as to create the reverse traveling wave signal on the transmission line.
In accordance with further aspects of the present invention, the forward traveling wave signal and the reverse traveling wave signal are beneficially tapped from the transmission line via a non-contact coupler such as, for example, directional coupler.
In accordance with still further aspects of the present invention, the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations are beneficially combined by adding the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations. The forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations may be conditioned prior to their being added.
Alternatively, the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations are beneficially combined by multiplying the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations such that the corresponding plurality of clock signals each have twice the common frequency and the common phase.
Alternatively still, the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations are beneficially combined by first summing the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations so as to provide a plurality of summed signals. Also, the forward traveling wave signal and the reverse traveling wave signal that are tapped from the transmission line at each of the plurality of different locations are differenced so as to provide a plurality of differenced signals. Then, each of the plurality of summed signals are squared, and each of the plurality of differenced signals are squared. Then, each squared summed signal and each corresponding squared differenced signal are differenced such that the corresponding plurality of clock signals each have twice the common frequency and the common phase.
In accordance with still further aspects of the present invention, the length of the transmission line is set so as to set a delay of the plurality of clock signals with respect to the forward traveling wave signal or the reverse traveling wave signal.
In another embodiment, the technique is realized by providing a first periodic signal on a first transmission line and a second periodic signal on a second transmission line, wherein the first periodic signal and the second periodic signal each have a common frequency and a constant relative phase. The first periodic signal is tapped off the first transmission line and the second periodic signal is tapped off the second transmission line at a plurality of different corresponding locations. The first periodic signal and the second periodic signal that are tapped off the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations are then combined so as to form a corresponding plurality of clock signals each having a common phase. The plurality of clock signals each have a frequency that is twice the common frequency.
In accordance with other aspects of the present invention, the first periodic signal is provided on the first transmission line and the second periodic signal on the second transmission line by generating the first periodic signal and generating the second periodic signal (e.g., by signal generators). Alternatively, a common periodic signal may be generated, and the first transmission line may be terminated with a short circuit and the second transmission line may be terminated with an open circuit.
In accordance with further aspects of the present invention, the first periodic signal and the second periodic signal may be tapped off the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations via non-contact couplers such as, for example, capacitive or inductive couplers, or direct-contact couplers such as, for example, resistive couplers.
In accordance with still further aspects of the present invention, the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations are beneficially combined by multiplying the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations such that the corresponding plurality of clock signals each have twice the common frequency and the common phase.
Alternatively, the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations are beneficially combined by first squaring the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations. Each squared first periodic signal and each corresponding squared second periodic signal are then differenced such that the corresponding plurality of clock signals each have twice the common frequency and the common phase.
Alternatively still, the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations are beneficially combined by first summing the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations so as to provide a plurality of summed signals. Also, the first periodic signal and the second periodic signal that are tapped from the first transmission line and the second transmission line, respectively, at each of the plurality of different corresponding locations are differenced so as to provide a plurality of differenced signals. Then, each of the plurality of summed signals are squared, and each of the plurality of differenced signals are squared. Then, each squared summed signal and each corresponding squared differenced signal are differenced such that the corresponding plurality of clock signals each have twice the common frequency and the common phase.
In accordance with still further aspects of the present invention, a delay between the first periodic signal and the second periodic signal is set so as to set a delay of the plurality of clock signals with respect to the first periodic signal or the second periodic signal.
The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.